Abstract
For diagnostic purposes micrometer-sized particles can be used as floating electrostatic
probes. Once injected into a complex rf plasma, these particles will become negatively
charged and can be trapped in the plasma sheath due to an equilibrium of several forces
working on them, e.g. the electrostatic force, gravity, drag forces and thermophoresis.
Measuring for example the position of the particles in the plasma sheath and the
interparticle distance while varying plasma parameters (power, pressure, temperature, gas
etc.) gives important information about plasma properties like the ion flux and the sheath
potential.
We experimentally investigated the behavior of micrometer sized particles inserted and
trapped in a rf plasma under varying gravity conditions in a centrifuge. Here we present
first results of those measurements. The experiments were carried out in a Perspex box
containing a parallel plate capacitive coupled rf argon plasma at pressures between 20 and
115 Pa. The typical forward power applied to the bottom electrode was ~10 Watt. The
squared electrodes are separated 5 cm from each other and both contain centered holes in
order to trap the particles in the created potential well. This also gives possibilities to
observe particle behavior from below. The monodisperse particles which are made of
melamineformaldehyde and have sizes ranging from 5 up to 12 µm are illuminated by an
expanded 532 nm laser beam. The height of the particles on which the forces are in
equilibrium is measured from pictures collected with an on-board CCD camera. This
whole setup is mounted on a centrifuge originally developed to study high pressure metal
halide lamps under hyper gravity conditions [1].
Results show that under these conditions particles can be trapped in the plasma sheath
when the gravitational force is 2.6g or less. When larger acceleration forces are applied
the particles are lost from the discharge. Due to the increased apparent gravity of the
particles in the centrifuge the height of the cloud above the powered bottom electrode
decreases with ~2 mm when the acceleration force is increased from 1g up to 2.6g
Original language | English |
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Title of host publication | Proceedings of the 21th NNV-Symposium Plasma Physics & Radiation Technology 2009, 3-4 March 2009, Lunteren, The Netherlands |
Place of Publication | Lunteren, The Netherlands |
Pages | B3- |
Publication status | Published - 2009 |
Event | 21st NNV Symposium on Plasma Physics and Radiation Technology - De Werelt, Lunteren, Netherlands Duration: 3 Mar 2009 → 4 Mar 2009 https://www.tue.nl/fileadmin/content/faculteiten/tn/PMP/Research/Conferences___Workshops/21st_NNV_symposium.pdf |
Conference
Conference | 21st NNV Symposium on Plasma Physics and Radiation Technology |
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Country/Territory | Netherlands |
City | Lunteren |
Period | 3/03/09 → 4/03/09 |
Other | |
Internet address |